Flame retardant products

ABSTRACT

A composition of matter (host material) has embodied therein a flame retardant material which comprises a combination of a phosphorus containing material which decomposes to produce phosphoric acid when exposed to flame (e.g. ammonium polyphosphate and/or melamine phosphate) and an oxygenated heterocyclic thermoplastic resin (e.g. an aldehyde resin). A blowing agent (e.g. melamine) also may be included in the flame retardant material. The thermoplastic resin encapsulates the other ingredients thus making the flame retardant melt blendable with the host material (e.g. thermoplastic polymers, thermosetting polymers, solvented systems, paper and reconstituted wood products) in which it is incorporated.

This invention relates to flame retardant products.

Flame retardant products exhibiting intumescent properties are wellknown. Such flame retardant products are incorporated in manycompositions of matter, (host materials), especially thermoplasticpolymer compositions. One such flame retardant product is a blend of aphosphoric acid producing catalyst, a charring agent and a blowingagent. The catalyst is a compound, e.g. ammonium polyphosphate, whichwhen exposed to flame yields phosphoric acid. The charring agent can bea polyhydric alcohol, e.g. pentaerythritol, which decomposes and reactswith phosphoric acid to form a carbonaceous char. The blowing agent,e.g. melamine, when exposed to flame produces a non-flammable gas (e.g.N₂) which serves to foam and expand the carbonaceous char.

The above mentioned three component flame retardant products are powderadditives which have processing limitations as they do not blend wellwith many compositions of matter (host materials), e.g. thermoplastics.In order to overcome these processing problems there have been attemptsto encapsulate the flame retardant additives in inert polymers. However,there is a disadvantageous limit on the amount of such encapsulatedflame retardant product that can be incorporated in the host materialsand the encapsulants themselves are generally flammable materials.

Proprietary flame retardant products have appeared on the market whichtypically are reaction products of pentaerythritol and phosphate esters.These flame retardant products are melt blendable with host materialssuch as thermoplastic polymers. However, such proprietary flameretardant products have to be used in combination with other flameretardants. Furthermore, such proprietary materials do not containblowing agents and so do not have the advantages of char foaming andexpanding.

Conventional flame retardant compositions are described in the followingprior art. WO 98/08898 discloses thermosetting resin coatings, (e.g.melamine formaldehyde), for flame retardant compositions. Thesethermosetting coatings are there purely for their physical effect whichis to lower the surface tension of the encapsulated flame retardantparticles to that of host polymers.

EP 0149813A discloses a flame proofed thermoplastic moulding material(e.g. styrene polymers) which contains a three component flame retardantmixture of phenol formaldehyde resins; a nitrogen containing organiccompound (e.g. urea) and a phosphorus containing organic compound. Thephenol formaldehyde resin is a thermosetting resin which is included forits thermodynamic properties.

EP 0033361A describes the coating of the flame retardant ammoniumphosphate with a condensation product of melamine and formaldehyde whichis a thermosetting resin. The melamine formaldehyde resin serves toprovide a waterproof coating for the ammonium phosphate. EP 0035094Amakes a similar disclosure to EP 0033361 A.

U.S. Pat. No. 5,643,980 discloses a flame retardant thermoplastic resin(e.g. a polyolefin) which contains a polyhydric alcohol-boric acidcomplex as a filler (e.g. a pentaerythritol complex) and theconventional flame retardant materials ammonium polyphosphate andmelamine (or melamine derivatives).

GB 1538093 relates to aqueous compositions and intumescent foams (e.g.polyurethane forms) made therefrom comprising a urea formaldehyde resinas filler, phosphorous acid as a hardener and a carbonate of analiphatic, araliphatic, heterocyclic-aliphatic or heterocyclic amine asa blowing agent. The urea formaldehyde resin is a thermosetting resin.

DE 2800891A discloses a self-extinguishing polymeric composition whichcontains as a flame retardant additive, a mixture of an ammonium oramine phosphate, a polyamide and a urea formaldehyde thermosettingresin. The polyamide is essential for flame retardant activity.

GB 1286192A discloses a thermosetting polymeric composition havingconventional intumescent ingredients.

An object of the present invention is to provide a unique flameretardant product which overcomes the problems of known flame retardantproducts in that it is more readily blendable with many compositions ofmatter (host materials), particularly thermoplastic compositions, andthus imparts a higher degree of flame retardancy to the host materials.

According to the present invention, there is provided a flame retardantcomposition which comprises a mixture of a phosphorus containingcompound which decomposes to produce phosphoric acid when exposed toflame and an oxygenated heterocyclic thermoplastic resin which isprepared by reacting an urea of the general formula (I)

where X is oxygen or sulphur and R¹ and R² are hydrogen, identical ordifferent alkyl of 1 to 18 carbon atoms, aryl of 6 to 9 carbon atoms oraralkyl of 7 to 9 carbon atoms or may be an alkyleneurea radical, wherealkylene is of 1 to 9 carbon atoms, with at least 2 moles of a CH-acidicaldehyde of the formula (II)

where R³ is hydrogen and R⁴ is alkyl, aryl or aralkyl, or R³ and R⁴ areidentical or different alkyl, aryl or aralkyl, in the presence of astrong acid, to give a condensation product, and thereafter treating theproduct with an alkali metal alcoholate in an anhydrous medium.

Preferably, R³ and R⁴ in the compound of general formula (II) is alkylof 1 to 10 carbon atoms, aryl of 6 to 9 carbon atoms or aralkyl of 7 to9 carbon atoms.

Further preferably, the compound of general formula (I) is urea and thecompound of general formula (II) is isobutyroaldehyde.

The phosphorus containing material preferably is selected from ammoniumpolyphosphate, sodium polyphosphate, potassium polyphosphate, melaminepolyphosphate, melamine phosphate or mixtures thereof.

Advantageously, the phosphorus containing material is a mixture ofammonium polyphosphate and melamine phosphate.

The flame retardant composition may contain a blowing agent, suitablymelamine or urea.

Preferably, the phosphorus containing material is encapsulated in theoxygenated heterocyclic thermoplastic resin.

Further preferably, the blowing agent and other ingredients of the flameretardant material are encapsulated in the oxygenated heterocyclicthermoplastic resin.

In this specification, the oxygenated heterocyclic thermoplastic resinis a resin prepared according to the process described in U.S. Pat. No.4,220,751 (BASF) wherein the resin is a condensation product of an ureaand a CH-acidic aldehyde. CH-acidic aldehydes are those where the carbonadjacent to the carbonyl group carries one or two hydrogen atoms.

In a preferred embodiment of the invention, the flame retardantcomposition comprises 25 to 60% by weight oxygenated heterocyclicthermoplastic resin; 0 to 75% by weight ammonium polyphosphate; 0 to 75%by weight melamine phosphate; and 0 to 45% by weight melamine with theproviso that ammonium polyphosphate or melamine phosphate essentially ispresent.

From another aspect the present invention is a composition of mattercontaining the flame retardant composition described and claimed herein.

The composition of matter may contain an amount of 5 to 90% by weight,preferably 10 to 45% by weight of the flame retardant composition.Higher inclusions may be desirable for masterbatches and systemsrequiring higher intumescent functionality.

Suitable compositions of matter (host materials), include thermoplasticpolymers, thermosetting polymers, paper, reconstituted wood products andsolvented systems (i.e. where the flame retardant material is dissolvedin a solvent or mixtures of solvents).

Preferred host materials are polyolefins, particularly polypropylene.

From yet another aspect, the present invention is an article made fromthe composition of matter described above. Such articles can be made bycompression moulding or injection moulding.

From yet another aspect, the present invention is a method of improvingthe flame retardant capability of a composition of matter by embodyingin the composition of matter a flame retardant composition as describedabove.

Compositions of matter containing the flame retardant composition of theinvention can be used in the manufacture of a wide variety of productsand components for use in the electronic, construction and transportindustries and can be incorporated into many structures including firedoors, vehicle passenger compartments, aircraft passenger and cargoareas as well as cargo storage containers and aircraft galley equipment,railway and underground carriages, cable trays (to prevent both loss ofsignal through the cable and passage of fire and heat along the cabletray itself), marine bulkheads, compressed gas and building structures.

Embodiments of the invention will now be described by way of example.

In the following examples of the invention the host material ispolypropylene. The examples show that the Limiting Oxygen Index (LOI) ofpolypropylene incorporating the flame retardant material of theinvention is increased. Since oxygen forms approximately 21% of normalatmosphere, thermoplastic polymers which have an LOI of 21% or lessusually burn freely in air. If the inclusion of a material into thepolymer increases the LOI of the polymer then this means that somedegree of flame retardance is imparted to the polymer. As the LOI of thepolymer increases above 21% then the polymer becomes increasinglydifficult to ignite and also increasingly likely to self extinguish.Generally speaking, once the LOI increases to above 30% then the polymerin effect is considered to be non-flammable and an LOI of 25% indicatesgood flame retardancy.

Successful polypropylene formulations containing a variety of examplesof the flame retardant material of the invention are illustrated in theTables below. All of the formulations contain the essential ingredients(a) the thermoplastic resin and (b) the phosphoric acid source (ammoniumpolyphosphate and/or melamine phosphate and some of the formulationsalso include melamine as a blowing agent).

The flame retardant material of the invention is not a simplecombination of the powdered components but rather it is an extrudate.The ammonium polyphosphate, melamine phosphate and melamine areeffectively encapsulated in the oxygenated heterocyclic thermoplasticresin during the extrusion process. This extrudate is normally producedas a chip (but with different equipment it could be made as a pellet orprill if required). The chip can be milled to a powder if this isconsidered desirable.

The finished flame retardant material has the appearance of a piece ofdull white plastic. The product is virtually dust free and the chip sizecan be varied to suit end use requirements. The flame retardant materialof the invention is a melt blendable product. The oxygenatedheterocyclic thermoplastic resin casing is both part of the integralflame retardant mechanism but also makes the product melt blendable withmany host materials. Compared to the traditional blends of flameretardants there is no pentaerythritol present. The oxygenatedheterocyclic thermoplastic resin is the charring agent as well as givingthe flame retardant material its melt blendable property.

It is to be noted that the flame retardant material of the invention isnot a reaction product of its ingredients but rather is a physical blendof the ingredients. To our knowledge, no other non-halogen flameretardant uses this method of having an oxygenated heterocyclicthermoplastic resin incorporated which is part of the flame retardantsystem. Other flame retardant systems normally use inert polymers toeither encapsulate the products or as an inert backbone onto which theflame retardant molecule is grafted.

In Table 1 below, the test samples are two and three component samplesproduced by compression and in Table 2, the test samples are fourcomponent samples produced by injection. Table 3 shows UL94 VerticalBurning Tests of polypropylene with various loadings of the fourcomponent sample of Example 9.

In the Tables, the following terms have the following meanings:

-   -   PP means polypropylene    -   APP means ammonium polyphosphate    -   MP means melamine phosphate    -   the “Level” column indicates the % w/w inclusion of the flame        retardant product in untreated polypropylene.    -   MFI refers to the Melt Flow Index—this gives an indication of        how difficult the flame retardant addition makes the resulting        polymer composition to process (in general the lower the MFI,        the more difficult the polymer composition is to process). The        MFI conditions were 230° C. and a weight of 2.16 kg.    -   UL94 refers to a standard test of the Underwriters Laboratory.

The ammonium polyphosphate used in the examples was Exolit AP422 fromClariant. The oxygenated heterocyclic thermoplastic resin used wasLaropal A81 which is an aldehyde resin obtained from BASF. The aldehyderesin, Laropal A101, again obtainable from BASF also could be used.

The melamine phosphate used was Melapur MP obtainable from CibaSpeciality Chemicals. The melamine phosphate provides both a phosphoricacid source for the char formation and a source of melamine and soprovides dual function.

The quantities expressed in the Tables are weight percentages. TABLE 1Aldehyde Example Resin APP MP Melamine Level LOI Blank 0 0 0 0 0 17 PP 140 0 60 0 20 19 2 40 40 0 20 20 21 3 40 40 20 0 20 23 4 35 65 0 0 2022.5 5 45 55 0 0 20 20

TABLE 2 Exam- Aldehyde UL94 ple Resin APP MP Melamine Level LOI (1.6 mm)6 40 40 10 10 30 24.8 Full Burn 7 35 55 5 5 30 31.3 Full Burn 8 35 45 1010 30 31.3 V0 9 35 50 7.5 7.5 30 33.2 V0

TABLE 3 Specimen Dimensions (mm): Length: 125 Width:  13 Thickness:  0.8Conditioning Procedure: 230° C. and 50% relative humidity UI94 VerticalBurning Test Burned Afterflame Afterflame Total to the CottonClassification Sample Time 1 (s) Time (s) Time (s) clamp ignited SingleOverall 20% 1 0 1 N Y V-2 V-2 Ex. 9 0 0 0 N Y V-2 0 0 0 N Y V-2 0 0 0 NY V-2 0 0 0 N N V-0 Total: 1 Av: 0 25% 0 0 0 N Y V-2 V-2 Ex. 9 0 0 0 N NV-0 0 0 0 N N V-0 0 0 0 N N V-0 0 0 0 N N V-0 Total: 0 Av: 0 25% 0 0 0 NN V-0 V-0 Ex. 9 0 0 0 N N V-0 REPEAT 0 0 0 N N V-0 0 0 0 N N V-0 0 0 0 NN V-0 Total: 0 Av: 0 30% 0 0 0 N N V-0 V-0 Ex. 9 0 0 0 N N V-0 0 0 0 N NV-0 0 0 0 N N V-0 0 0 0 N N V-0 Total: 0 Av: 0Observations from the Tables

-   -   (i) It is possible to improve the LOI of polypropylene using an        intumescent system comprising only two components (aldehyde        resin+MP—Ex 1) and (aldehyde resin+APP—Examples 4 & 5).    -   It is also possible to improve the LOI of polypropylene with        three component systems (Examples 2 and 3).    -   (iii) The most successful results are with four component        intumescent systems Examples 6, 7, 8 and 9).    -   (iv) Table 2 shows that formulations can be prepared to achieve        LOI results of 33.2.    -   (v) Table 3 shows that UL94 VO ratings can be achieved at a        thickness of 0.8 mm.

There now follows graphs depicting the smoke reduction, heat release andMFI properties of the flame retardant product of the invention. In thegraphs, the flame retardant product designated 457X is the fourcomponent sample of Example 9 in Table 2.

-   -   Cone Calorimeter Cumulative Smoke Results (50 kW)    -   Flame retardant of Example 9 incorporated at 30% in        polypropylene. BRFR is a polypropylene flame retarded with 21%        decabromo diphenyl ether and 12% antimony trioxide.    -   Cone Calorimeter Cumulative Smoke Results (50 kW)    -   PP=Polypropylene, flame retardant of Example 9 included at 25%        and 30% in PP

The Graphs A and B above show the significant reduction in cumulativesmoke, which can be achieved when the flame retardant product of theinvention is incorporated in PP. The smoke produced from the polymer canbe reduced by up to 75%. More significantly however, when compared tobrominated flame retardants systems, the invention produces only 2% ofthe total smoke evolved from the brominated systems. This is anextremely important factor as while a fire is developing, smoke is asbig a threat to life as the fire is itself.

-   -   Cone Calorimeter Heat Release Rates (50 kW)    -   PP=Polypropylene. Flame retardant of Example 9 incorporated at        30% in polypropylene. BRFR is a polypropylene flame retarded        with 21% decabromo diphenyl ether and 12% antimony trioxide.

Graph C shows the heat release rates for three systems, untreated PP, PPtreated with brominated flame retardants and PP treated with the flameretardant invention. The heat release rate is important as it shows howmuch energy a system will add to the development of a fire. Theuntreated PP shows a significant peak after 100s, which demonstrates itwill contribute significantly to any fire development in the earlystages. The brominated flame retardant works by increasing theresistance to ignition, which is demonstrated in the graph by the delayin reaching the peak HRR by 60 seconds. However, once ignited thissystem liberates as much energy as the untreated PP at the maximum HRRpeak. The system containing the flame retardant of the invention showsno significant peak in the HRR and plateaus at a level 70% below thepeak HRRs of the untreated PP and brominated flame retardant systems.This demonstrates that the flame retardant of the invention whenincorporated in a polymer will not only help increase the resistance toignitability but will also reduce the contribution the polymer will maketo the development of a fire.

-   -   Melt Flow Index (MFI) Comparisons (230° C., 2.19 kg)    -   Polymer=polypropylene, flame retardant of Example 9 included at        25% and 30% in PP.

Melt Flow Index measures the amount of polymer which can be extruded ina 10 minute period, for a given temperature and force/weight.Essentially this can be considered as a measure of how easily a givenpolymer can be processed, the higher the value the easier processingshould be. Graph D shows the effect of adding the flame retardant of theinvention to PP. In general the addition of the flame retardant of theinvention will increase the MFI, so making it easier to process thepolymer.

1. A flame retardant composition which comprises a mixture of aphosphorus containing compound which decomposes to produce phosphoricacid when exposed to flame and an oxygenated thermoplastic heterocyclicresin which is prepared by reacting an urea of the general formula (I)

where X is oxygen or sulphur and R¹ and R² are hydrogen, identical ordifferent alkyl of 1 to 18 carbon atoms, aryl of 6 to 9 carbon atoms oraralkyl of 7 to 9 carbon atoms or may be an alkyleneurea radical, wherealkylene is of 1 to 9 carbon atoms, with at least 2 moles of a CH-acidicaldehyde of the formula (II)

where R³ is hydrogen and R⁴ is alkyl, aryl or aralkyl, or R³ and R⁴ areidentical or different alkyl, aryl or aralkyl, in the presence of astrong acid, to give a condensation product, and thereafter treating theproduct with an alkali metal alcoholate in an anhydrous medium.
 2. Aflame retardant composition as claimed in claim 1 wherein the compoundof general formula (I) is urea.
 3. A flame retardant composition asclaimed in claim 1 wherein R³ and R⁴ in the compound of general formula(II) is alkyl of 1 to 10 carbon atoms, aryl of 6 to 9 carbon atoms oraralkyl of 7 to 9 carbon atoms.
 4. A flame retardant composition asclaimed in claim 1 wherein the compound of general formula (I) isisobutyroaldehyde.
 5. A flame retardant composition as claimed in claim1 wherein the phosphorus containing material is selected from ammoniumpolyphosphate, sodium polyphosphate, potassium polyphosphate, melaminepolyphosphate or mixtures thereof.
 6. A flame retardant composition asclaimed in claim 5 wherein the phosphorus containing material is amixture of ammonium polyphosphate and melamine phosphate.
 7. A flameretardant composition as claimed in claim 1 which contains a blowingagent which produces a non-flammable gas when exposed to flame.
 8. Aflame retardant composition as claimed in claim 7 wherein the blowingagent is melamine or urea.
 9. A flame retardant composition as claimedin claim 1 wherein the phosphorous containing material is encapsulatedin the oxygenated heterocyclic thermoplastic resin.
 10. A flameretardant composition as claimed in claim 7 wherein the blowing agentalso is encapsulated in the oxygenated heterocyclic thermoplastic resin.11. A flame retardant composition as claimed in claim 1 which isprepared by extrusion.
 12. A flame retardant composition as claimed inclaim 1 wherein the flame retardant composition comprises 25 to 60% byweight oxygenated heterocyclic thermoplastic resin; 0 to 75% by weightammonium polyphosphate; 0 to 75% by weight melamine phosphate and 0 to45% by weight melamine with the proviso that ammonium polyphosphate ormelamine phosphate essentially is present.
 13. A composition of matterwhich contains a flame retardant composition as claimed in claim
 1. 14.A composition of matter as claimed in claim 13 wherein the flameretardant composition is present in the composition of matter in anamount of 5 to 90% by weight.
 15. A composition of matter as claimed inclaim 14 wherein the flame retardant composition is present in thecomposition of matter in an amount of 10 to 45% by weight.
 16. Acomposition of matter as claimed in claim 13 selected from thermoplasticpolymers, thermosetting polymers, paper, reconstituted wood products andsolvented systems.
 17. A composition of matter as claimed in claim 16which is a polyolefin.
 18. A composition of matter as claimed in claim17 wherein the polyolefin is polypropylene.
 19. An article formed from acomposition of matter as claimed in claim
 13. 20. An article as claimedin claim 19 formed by injection moulding or compression moulding.
 21. Amethod of improving the flame retardant capability of a composition ofmatter by embodying in the composition of matter a flame retardantcomposition as claimed in claim 1.